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1 Danaus plexippus North American monarch Conservation Plan Plan de América del Norte para la conservación de la mariposa monarca Plan nord-américain de conservation du monarque

2 This publication was prepared by the Secretariat of the Commission for Environmental Cooperation (CEC) and does not necessarily reflect the views of the governments of Canada, Mexico or the United States of America. Reproduction of this document in whole or in part and in any form for educational or non-profit purposes may be made without special permission from the CEC Secretariat, provided acknowledgement of the source is made. The CEC would appreciate receiving a copy of any publication or material that uses this document as a source. Published by the Communications Department of the CEC Secretariat. La presente publicación fue elaborada por el Secretariado de la Comisión para la Cooperación Ambiental y no necesariamente refleja las opiniones de los gobiernos de Canadá, Estados Unidos o México. Se permite la reproducción total o parcial de este documento, en cualquier forma o medio, con propósitos educativos y sin fines de lucro, sin que sea necesario obtener autorización expresa por parte del Secretariado de la CCA, siempre y cuando se cite debidamente la fuente. La CCA apreciará se le envíe una copia de toda publicación o material que utilice este documento como fuente. Edición al cuidado del Departamento de Comunicación y Difusión Pública del Secretariado de la CCA. La présente publication a été préparée par le Secrétariat de la CCE et ne reflète pas nécessairement les vues des gouvernements du Canada, du Mexique ou des États-Unis. Cette publication peut être reproduite en tout ou en partie sous n importe quelle forme, sans le consentement préalable du Secrétariat de la CCE, mais à condition que ce soit à des fins éducatives et non lucratives et que la source soit mentionnée. La CCE apprécierait recevoir un exemplaire de toute publication ou de tout écrit inspiré du présent document. Publié par la section des communications du Secrétariat de la CCE. Publication details Type: Project report Date: June 2008 Original language: English Review and Quality Assurance Procedures Peer review: February 2008 Review by the Parties: March April 2008 For more information please consult the Acknowledgements. Particularidades de la publicación: Tipo: informe de proyecto Fecha: junio de 2008 Idioma original: inglés Procedimientos de revisión y aseguramiento de calidad: Revisión de especialistas: febrero de 2008 Revisión de las Partes: marzo abril de Para información adicional, consúltense los agradecimientos. Renseignements sur la publication Type de publication : rapport de projet Date de parution : juin 2008 Langue d origine : anglais Procédures d examen et d assurance de la qualité : Examen par les pairs : février 2008 Examen par les Parties : de mars 2008 à avril 2008 Pour de plus amples renseignements, prière de consulter la section «Remerciements». Commission for Environmental Cooperation 393, rue St-Jacques Ouest, bureau 200 Montreal (Quebec) Canada H2Y 1N9 info@cec.org Commission for Environmental Cooperation, 2008 ISBN Dépôt légal Bibliothèque et Archives nationales du Québec, 2008 Dépôt légal Bibliothèque et Archives Canada, 2008 Printed in Canada Comisión para la Cooperación Ambiental 393, rue St-Jacques Ouest, bureau 200 Montreal (Quebec) Canadá H2Y 1N9 info@cec.org Comisión para la Cooperación Ambiental, 2008 ISBN Dépôt légal Bibliothèque et Archives nationales du Québec, 2008 Dépôt légal Bibliothèque et Archives Canada, 2008 Impreso en Canadá Commission de coopération environnementale 393, rue St-Jacques Ouest, bureau 200 Montréal (Québec) Canada H2Y 1N9 info@cec.org Commission de coopération environnementale, 2008 ISBN Dépôt légal Bibliothèque et Archives nationales du Québec, 2008 Dépôt légal Bibliothèque et Archives Canada, 2008 Imprimé au Canada

3 North American Monarch conservation Plan 2 Plan de América del Norte para la conservación de la mariposa monarca 52 Plan nord-américain de conservation du Monarque 106 Commission for Environmental Cooperation Comisión para la Cooperación Ambiental Commission de coopération environnementale

4 North American Monarch Conservation Plan Monarch butterfly Danaus plexippus

5 Table of contents PREFACE 5 1 Executive summary 9 2 Background 10 2 Description of Species Adults Eggs Larvae Pupae 13 4 Host Plants: Milkweed 13 5 The Monarch Butterfly s Annual Life Cycle Migration Overwintering 16 6 World-wide DistributioN 19 7 Discovery of the Overwintering Sites 19 8 Current Status and ConditioN Eastern Populations Western Populations 23 9 Current Factors Causing Loss or Decline Breeding Habitat Loss and Degradation Wintering Habitat Loss and Degradation Disease and Parasites Climate Change Pesticide Use Legal Status, Management and ActioN International Canada United States Mexico Public and Commercial Perception and Attitudes trinational Conservation: Goals, Objectives and Target Actions Specific Objectives of the Monarch Conservation Plan Table of Specific Actions References Appendix: List of Acronyms 51

6 monarch FACT SHEET p pcommon name: Monarch Butterfly p pscientific name: Danaus plexippus p pstatus: Not an endangered species IUCN recognizes the monarch migration as an endangered phenomenon. p pdescription: p phabitat: p prange: Large nymphalid butterfly (wingspan of 9 10 cm) Warning coloration: orange and black Toxic to most vertebrates with cardiac glycosides obtained from milkweed (Asclepias spp.) Sexually dimorphic. Black veins are thicker on the female s wings and the male has small pouches on its hind wings where it stores pheromones. Large populations spend the summer in temperate regions and migrate south to Mexico to spend the winter. There are small resident populations in Mexico. The monarch butterfly is a species with tropical origins. Temperate to tropical regions Anywhere milkweed grows Fir, pine, oak and cedar forests during hibernation Secondary vegetation Disturbed habitats like roadsides and the surroundings of agricultural fields In America: southern Canada to Central and South America In North America: at least three populations (Eastern, Western, and Mexican residents) Western population from British Columbia to California Eastern population from southern Canada and eastern United States (east of the Rockies) to central Mexico (Michoacán and the State of México). Some butterflies continue migration through Florida to the Caribbean Mexican resident population (scattered throughout Mexico) Through introductions in the 19th century, monarchs colonized sites in Australia, Indonesia, the Canary Islands and Spain p pmigration: Western population: Monarchs migrate in the fall from British Columbia, Washington, Oregon and other western states to roosting sites on the coast of California. Eastern population: Monarchs migrate south during the fall from southeastern Canada and the eastern United States to their wintering sites in central Mexico, and re-colonize their breeding range in Texas in the spring. During hibernation they concentrate in very small areas. p plife stages: Egg Larva, caterpillar Pupa, chrysalis Adult, imago p pdiet: Larvae feed only on leaves of milkweed (Asclepias spp). In this, they are strict specialists. Adults are generalists that feed on a wide variety of flowers, flower nectar and water. p plife span: Adult life span varies from less than a month to nine months. Adults from spring and summer cohorts live about four weeks. However, the migratory generation can live up to nine months (Methuselah generation) and carry out the two-way trip. The boreal limits of the monarch distribution are reached by the second or third generation. p pimpacts and Threats: Habitat destruction and fragmentation throughout the flyway, especially in overwintering and breeding sites Habitat loss through urbanization Use of toxic agrochemicals Reduction of milkweed populations Genetically modified organisms (GMOs), like soybeans, that tolerate herbicides (Asclepias does not) Parasites (viruses, bacteria and protozoa) Climate change Lack of information/lack of environmental education 4

7 Preface The 1994 North American Agreement on Environmental Cooperation, establishing the Commission for Environmental Cooperation (CEC), expresses the commitment of Canada, Mexico and the United states to increase cooperation to better conserve, protect and enhance the environment, including wild flora and fauna. The CEC s 2003 Strategic Plan for North American Cooperation in the Conservation of Biodiversity strengthens this commitment with an integrated perspective for conservation and sustainable use of biological resources. This North American Monarch Conservation Plan (NAMCP) is part of the effort to support and complement existing initiatives to maintain healthy monarch populations and habitats throughout the migration flyway. The monarch butterfly: An opportunity for continental success Following Dr. Fred Urquhart s identification of the wintering location of the monarch butterfly in the volcanic mountains of south-central Mexico more than 30 years ago, the phenomenon of their astonishing migratory journey became well known. This fragile, amazing creature, known to every child, became a sort of trinational emissary representative of our common natural heritage and, consequently, of our shared responsibility to protect that heritage. Each country in North America contains some combination of habitats in which monarchs breed, migrate and overwinter, and at each of these stages they require different resources. Any weak link in the chain of habitats threatens the integrity of the entire migratory phenomenon. And, just as these habitats differ, the socioeconomic and cultural characteristics of the places vary too, requiring different but complementary strategies. Recognizing our shared responsibility and differences, this trinational initiative is intended to enhance through coordinated action the effectiveness of conservation measures undertaken in each country to conserve this rare phenomenon. Ensuring conservation: Promoting sustainable local livelihoods As with many endangered species and natural phenomena, the monarch faces different threats throughout its migratory flyway, ranging from the disappearance of overwintering habitat, predation, to the impact of herbicides and insecticides in their breeding range. Each of these stressors presents itself in different economic, social and institutional contexts. This monarch conservation plan acknowledges that in order to be successful and enduring, it must thus address some of the local socio-economic challenges and incorporate innovative approaches to promote sustainable local livelihoods. 5

8 The North American Monarch Conservation Plan On 27 June 2007, the CEC Council instructed the Secretariat, to support the existing multi-stakeholder, collaborative effort to develop a North American Monarch Conservation Plan, with the aim of maintaining healthy monarch populations and habitats throughout the migration flyway supported by a Trilateral Monarch Butterfly Sister Area Network and local community involvement. As a result, the CEC hosted a trinational workshop in Morelia, Michoacán, in December 2007, and obtained input from an extensive list of experts from diverse backgrounds from Canada, Mexico and the United States. The preparation of this conservation plan has benefited from the valuable contributions and in-depth review of an extensive list of experts from diverse backgrounds from Canada, Mexico and the United States. This plan provides an updated account of the species and its current situation, identifies the main risk factors affecting it and its habitat throughout the flyway, and summarizes the current conservation actions taken in each country. Against this background, it offers a list of key trinational collaborative conservation actions, priorities and targets to be considered for adoption by the three countries. The actions identified address the following main objectives: (1) decrease or eliminate deforestation in the overwintering habitat; (2) address threats of habitat loss and degradation in the flyway; (3) address threats of loss, fragmentation and modification of breeding habitat; (4) develop innovative enabling approaches that promote sustainable livelihoods for the local population; and (5) monitor monarchs throughout the flyway. The adoption of measures to address these objectives will help conserve the monarch and its habitats for future generations. Acknowledgments There is a long history of research and cooperation among government agencies, nongovernmental organizations, the public, and the scientific community to promote monarch conservation. This plan would not be possible without their dedicated efforts. We owe an enormous debt of gratitude to the participants and experts who provided their wisdom and knowledge through participation in the various meetings and workshops (listed below) that led to the development of this plan. We thank the agencies and organizations who co-hosted workshops and meetings. We are especially grateful to Karen Oberhauser, from the University of Minnesota and the Monarch Butterfly Sanctuary, for her role as coordinator and principal author of the NAMCP. Co-authors include Donita Cotter, Donald Davis, Robert Décarie, Alberto Elton Behnumea, Carlos Galindo-Leal, María Pía Gallina Tessaro, Elizabeth Howard, Jean Lauriault, Wendi Macziewski, Stephen Malcolm, Felipe Martínez, Javier Medina González, Maria McRae, Dean Nernberg, Irene Pisanty Baruch, Isabel Ramírez, Juan José Reyes and Ali Wilson. Peer reviewers of subsequent drafts were Lincoln P. Brower, Exequiel Ezcurra, Scott Hoffman Black, Jürgen Hoth, Fiona Hunter, Felix Sperling and Orley Taylor Jr. We also take this opportunity to acknowledge the leadership and contribution of Conanp, in particular, the staff of the Monarch Butterfly Biosphere Reserve (MBBR). 6

9 We would like to thank the CEC s Biodiversity Conservation Working Group (BCWG) for their support for this initiative. We also acknowledge the individuals and organizations who contributed data and analyses, as well as all those too numerous to name to whom we owe a huge debt for their support and cooperation. Grateful thanks go to Karen Schmidt, Jeffrey Stoub, Johanne David, Jacqueline Fortson and Douglas Kirk, of the CEC, who greatly helped the development and preparation of this plan, which was coordinated by Hans Herrmann, CEC Senior Program Manager, Biodiversity. CEC s Trinational Experts Workshop: Developing a North American Monarch Butterfly Conservation Plan, Morelia, Michoacán, 5 7 December 2007 The Trinational Experts Workshop was organized by the Secretariat at the direction of the CEC Council through Resolution 07-09, Trinational cooperation to conserve the monarch buttefly and promote sustainable local livelihoods, to build upon the multi-stakeholder, collaborative NAMCP initiative launched at the 2006 Monarch Flyway Conservation Workshop. Participants: Sandra Baumgartner, Flavio Cházaro Ramírez, Donita Cotter, Tara Crewe, Alfredo Cruz Colín, Andrew Davis, Donald Davis, María Guadalupe del Río Pesado, Dennis Frey, Carlos Enrique Galindo Leal, Eligio García Serrano, Elizabeth Howard, Jean Lauriault, Francisco Luna Contreras, Stephen Malcolm, Felipe Martínez Meza, Concepción Miguel Martínez, Eneida Beatriz Montesinos Patiño, Irene Pisanty Baruch, Héctor Quintanilla Heredia, Oscar Manuel Ramírez Flores, María Isabel Ramírez Ramírez, Eduardo Rendón Salinas, Juan José Reyes Rodríguez, Douglas Taron, Juan Francisco Torres Origel, María del Rocío Treviño Ulloa, Brian Houseal (facilitator), Hans Hermann, Karen Schmidt. Monarch Flyway Conservation Workshop, Mission, Texas, 6 7 December 2006 The initiative to prepare an NAMCP was launched at the December 2006 Monarch Flyway Conservation Workshop in Mission, Texas. The workshop was sponsored by the US Forest Service (USFS) International Programs; US Aid for International Development (USAI); Texas Parks and Wildlife Department (TPWD); the Wildlife Trust; and City of McAllen, Texas. The workshop was attended by representatives of agencies, academia, and NGOs from the three countries. Participants: María Araujo, Lincoln Brower, Óscar Contreras Contreras, Donita Cotter, Carol Cullar, Don Davis, María Guadalupe del Río Pesado, Janet Ekstrum, Mike Engel, Dan Evans, Jesús Franco, Rebecca Goodwin, Mary Gustafson, Margee Haines, Richard Holthausen, Colleen Hook, Buddy Hudson, Mary Kennedy, Jean Lauriault, Carol Lively, Rolando Madrid, Helen Molina Sánchez, Sandra Nitchie, Karen Oberhauser, Mike Quinn, Jeff Raasch, Mike Rizo, Craig Rudolph, Phil Schappert, Evan Seed, Karen Shannon, Sue Sill, Chip Taylor, Carmen Téllez-O Mahony, Matt Wagner, Don Wilhelm, Juan Manuel Frausto Leyva, José Andrés García Almanza, Eligio García Serrano, Tomás Martínez Ramírez, Lidia Miranda Sánchez, Eduardo Rendón Salinas, Juan José Reyes Rodríguez, Alfonso Rojas Pizano, Alejandro Torres, Xicoténcatl Vega, Adriana Vlera-Bermejo, Tiburcio Ybarra Caballero. Workshop participants selected three representatives from each country to serve on a planning committee. The NAMCP Committee met twice to develop plan objectives and action items. 7

10 ppnamcp Committee at 4th Monarch Butterfly Regional Forum (Foro Monarca), Morelia, Michoacán, March 2007: María Araujo, Jean Lauriault, Carlos Galindo Leal, Concepcíón Miguel Martínez, Karen Oberhauser, Juan José Reyes Rodríguez. ppnamcp Committee at XII Meeting of the Canada/Mexico/US Trilateral Committee for Wildlife & Ecosystem Conservation and Management, Quebec City, Quebec, 13 May 2007: María Araujo, Donita Cotter, Donald Davis, María Pía Gallina Tessaro, Margee Haines, Karen Oberhauser, Irene Pisanty, Eduardo Rendón Salinas, Juan José Reyes Rodríguez, Mary Rothfels. Trilateral Monarch Butterfly Sister Protected Area Workshop, Morelia, Michoacán, March 2006 The initiative to establish a network of sister protected areas to collaborate on monarch conservation projects and seek CEC funding for a handbook of standardized monitoring protocols was launched at this workshop hosted by Mexico s National Commission of Natural Protected Areas (Conanp), the US Fish and Wildlife Service-National Wildlife Refuge System, and the Canadian Wildlife Service (CWS). Participants: Martín Arriaga Pérez, Paul Ashley, James Burnett, Donita Cotter, Alberto Elton Benhumea, María Pía Gallina Tessaro, Nancy Gilbertson, Mónica Herzig, Mike Higgins, Deborah Holle, Jean Lauriault, André Mailloux, Felípe Martínez Meza, Tim Menard, Concepción Miguel Martínez, Ruth Morales, Angélica Narváez, Arturo Peña, Lisa Petit, Carlos A. Sifuentes Lugo, Yurico Siqueiros Jhimada, Marian Stranak, Melida Tajbakhsh, Rocío Treviño and Héctor Zepeda. We trust the NAMCP will serve to enhance cooperation and networking among diverse sectors of society working on the well-being of the monarch and its habitats across North America. 8

11 1 Executive Summary The monarch butterfly (Danaus plexippus L.) may be the most well-known butterfly in the world. The migrations of monarch butterflies in North America to overwintering sites in Mexico and California are among the most spectacular and unusual of the world s natural events. However, habitat loss and degradation pose threats to both the eastern and western migratory populations of North American monarchs throughout their annual cycle of breeding, migrating and overwintering. The decline of the migratory phenomenon is certain unless these threats are addressed. Monarchs depend upon a wide range of habitats in Canada, the United States and Mexico, thus conservation of their migratory phenomenon requires trilateral cooperation. The North American Monarch Conservation Plan (NAMCP) is intended to provide a long-term cooperative agenda for conservation of the monarch butterfly. This document summarizes evidence of the rate of habitat loss during each stage of the monarch s annual cycle. The relatively small size of the wintering sites make the loss of these habitats, from commercial and subsistence-scale timber harvesting in Mexico and commercial and municipal development in California, of the most immediate concern. Recent analyses of the overwintering area document an accumulated disturbance of a fifth of the forested land in the Monarch Butterfly Biosphere Reserve (MBBR) in Mexico from 1986 to Changing farm practices and suburbanization of agricultural land in the United States are resulting in losses of approximately 876,000 hectares/ year of land that can support the host plants and nectar sources required for monarch reproduction and migration. Habitat conservation and restoration are absolutely necessary for monarch survival. Mexico, Canada and the United States must work together to ensure that: 1) sufficient suitable habitat is available on the overwintering grounds in the United States and Mexico for the populations to persist; and 2) sufficient breeding and migrating habitat is available in Canada, Mexico and the United States to maintain their current contribution to the overall North American population. The NAMCP is divided into eleven sections. The initial seven sections provide an updated account of the species and its current situation. The eighth section identifies the main causes of loss or decline and puts in perspective the ensuing sections, related to current management actions taken in each country, as well as public perception of the species. Against this background, the last section offers a list of key trinational collaborative conservation objectives and actions. The objectives which are of the most immediate importance and have the most potential for trilateral cooperation are as follows: Habitat conservation and restoration are absolutely necessary for monarch survival. ppdecrease or eliminate deforestation due to unsustainable logging and habitat conversion in the overwintering habitat. This objective must be accomplished through a combination of surveillance and enforcement of existing laws, prevention and mitigation actions, and support for alternative and sustainable forest management and economic practices. ppaddress threats of habitat loss and degradation in the flyway. Effective flyway conservation requires immediate management actions. These actions must be supported by research and monitoring to identify the habitat types and locations that are most important to monarchs during their spring and autumn migrations, and by an understanding of how human activities affect the availability and suitability of these habitats. 9

12 Although the species itself is not in danger of extinction, the North American migration is considered an endangered biological phenomenon due to threats to the monarch s habitats during its annual cycle of breeding, migrating and wintering. ppaddress threats of loss, fragmentation, and modification of breeding habitat. Breeding habitat conservation will require better understanding of monarch host plants, including how land use practices affect the distribution and abundance of numerous milkweed (Asclepias) species. Land use practices that support monarch breeding should be encouraged among government agencies, private conservation organizations, and public and private landowners. ppdevelop innovative enabling approaches. Incentives for conservation, such as payment for environmental services by the Monarch Butterfly Conservation Fund (within the Fondo Mexicano para la Conservación de la Naturaleza FMCN) in the MBBR, could help to mitigate threats due to habitat loss. Cooperative trilateral actions, such as supporting and expanding the network of sister protected areas involved in monarch conservation will protect habitat, support environmental education, and reinforce monitoring efforts. Such efforts should be expanded and duplicated in other areas and by other organizations. p pmonitor monarch population distribution, abundance, and habitat quality, including water availability. Government and nongovernmental agencies should support the development and dissemination of a monitoring program, and a diagnosis of biological and socioeconomic drivers of monarch population dynamics. Coordinated monitoring throughout the monarch s annual cycle and open sharing of the data are key to understanding the status of the population and effectiveness of conservation actions. 2 Background Probably the world s most familiar butterfly, the monarch (Danaus plexippus L.) has been the focus of research on insect and host plant interactions, insect defenses, mimicry, migration, reproductive physiology, overwintering biology, habitat conservation, community management, ecotourism, and many other topics. This butterfly is best known for the incredible migration made by the eastern North American population, in which individuals fly from summer breeding grounds located as far north as southern Canada to their overwintering habitat in central Mexico. Although the species itself is not in danger of extinction, the North American migration is considered an endangered biological phenomenon due to threats to the monarch s habitats during its annual cycle of breeding, migrating and wintering. Because monarchs depend upon a wide range of habitats in Canada, the United States and Mexico, conservation of the migratory phenomenon requires trilateral cooperation. 10

13 3 Description of Species Monarch butterflies are in the family Nymphalidae, sub-family Danainae. The monarch was named Papilio plexippus by Linnaeus in 1758 (Vane-Wright 2007). It is the type species of the genus Danaus, which was named by Kluk in While a recent catalogue of Latin American butterflies recognized six subspecies of D. plexippus (Lamas 2004), mitochondrial DNA sequences suggest that these groups are not genetically distinct (Brower and Jeansonne 2004) and at least one of the subspecies (D. plexippus megalippe) may mix in the Caribbean with migratory D. plexippus plexippus. Herein, we are concerned with the subspecies Danaus plexippus plexippus in Mexico, the United States and Canada. 3.1 Adults The adult monarch is a relatively large butterfly, with a wingspan of approximately 9 to 11 cm. Its bright orange wings have black veins, and black edges that contain white spots along the margin. The underside of the wings is duller orange, so that when the wings are folded in rest, the butterflies appear camouflaged as they cluster or rest singly in trees or on other substrates. The species is sexually dimorphic; males are slightly larger than females and have a black spot on each hindwing consisting of androconial scales. Pheromone-producing androconial scales are used, in related species, to attract mates. However, most researchers agree that chemical communication plays a less significant role in monarch butterflies, compared with other species in the same genus. Females lack the androconial patch, have slightly more brown scales in the orange patches of their wings, and more black scales over the wing veins, making the veins appear wider. Male and female adults 1 Female on black-eyed susan 2 Female abdomen showing abdominal slit 3 Male on zinnias 4 Male abdomen showing claspers

14 There are color variants in adult monarchs, most notably a variation (nivosus) in which the orange is replaced with white (Stimson and Meyers 1984). This color variation is caused by a single recessive gene, and has been found throughout the world, including Australia, New Zealand, Indonesia and the United States. It is extremely rare everywhere but Hawaii, where it sometimes comprises up to 10% of the population (Stimson and Berman 1990, Vane-Wright 1986). Viceroy (Limenitis archippus) Monarch adults are sometimes confused with related butterfly species, including D. gilippus (the queen butterfly), D. eresimus (the soldier butterfly) and D. erippus (the South American monarch), and with Limenitis archippus (the North American viceroy butterfly). Migratory North American monarchs undergo several generations per year. The summer generation adults live between two and five weeks. The late generation adults migrate, then overwinter at sites in central Mexico and California. These overwintering individuals live seven to nine months, without breeding and laying eggs until the following spring as they re-migrate toward their spring and summer breeding ranges. Egg on Asclepias syriaca (common milkweed) 3.2 Eggs Five larval instars and egg Monarch eggs are conical, with a flat base. They are approximately 1.2 millimeters (mm) tall by 0.9 mm in diameter at the widest point, and are a pale, yellow-cream color, with ridges running from the tip to the base. Monarchs only lay their eggs on milkweed plants. Adult females lay eggs singly, secreting a glue-like substance that adheres the egg to a milkweed plant. Wild females probably lay from 300 to 400 eggs over the course of their lifetime, although captive females can lay, on average, approximately 700 eggs in two to five weeks (Oberhauser 2004). The larvae emerge in three to five days, with shorter development times corresponding to warmer temperatures. 3.3 Larvae Monarch larvae (caterpillars) are white with black and yellow stripes and have two pairs of black filaments, on larval segments 2 and 11. Larvae undergo five instars (intervals between molts) over a period of nine to 13 days. While the bright color patterns on monarch larvae probably represent aposematic, or warning, coloration, monarchs in the egg and larval stages nonetheless suffer high rates of predation from invertebrate predators. Several studies have documented mortality rates of over 90% during these stages (reviewed in Zalucki et al. 2002, Prysby 2004). It appears that the chemical defense gained from ingesting toxic milkweed cardenolides (see Host Plants: Milkweed section, below) is more effective against vertebrate predators, although Rayor (2004) documented a preference by wasp predators for larvae that had fed on milkweed species having lower cardenolide levels. Once fifth instar larvae are fully grown, they leave their milkweed host plant to search for an elevated and usually well-hidden pupation site. 12

15 3.4 Pupae Monarch pupae (chrysalids) are about 3 centimeters (cm) long and are bright turquoise-green, with gold spots. These metallic-appearing spots are typical of the Danainae, and are caused by alternating dense and clear layers in the endocuticle (a layer in the exoskeleton). These layers reflect and transmit light differently, and cause constructive interference of light, making them look like shiny metal. The pupa stage lasts nine to 15 days under normal summer conditions. This is the least-studied stage of monarchs, due to the difficulty in finding pupae in the wild. This difficulty suggests that monarch pupae are cryptically colored, as opposed to the aposematic (bright warning) coloration exhibited by adults. On the last day as a pupa, the orange, black, and white patterns of the adult wings become visible through the pupal covering. Pupae 4 Host Plants: Milkweed Monarch larvae are obligate herbivores of milkweeds and are likely to feed on any of the approximately 115 species in the genus Asclepias in North America and the Caribbean (Malcolm et al. 1992, Malcolm 1994). This genus of perennial plants, with over 140 species world-wide, was also named, like the monarch, by Linnaeus. He named milkweeds after Asklepios, the Greek god of healing, because of their many folk-medicinal uses. Monarchs also feed on milkweed vines in the genera Sarcostemma, Cynanchum and Matelea (Ackery and Vane-Wright 1984). Until recently, these three genera and Asclepias were included in the family Asclepiadaceae, but the family is now treated as a subfamily in the dogbane family, Apocynaceae. In addition to being the larval food source for monarchs, their close relatives, and several other specialist insects, milkweeds are important nectar sources for many insects. Milkweed is named for its milky sap, which contains alkaloids and other complex compounds, including cardenolides. In Spanish, milkweed is known as venenillo (small poison) and algodoncillo (small cotton), due to the toxic nature of the plant and the appearance of the seeds. The milky sap, or latex, confers both mechanical and chemical defenses against potential herbivores (Malcolm et al. 1992, Malcolm 1994), but monarch larvae show a range of feeding behaviors that circumvent these latex defenses (Dussourd and Eisner 1987, Dussourd 1993, Zalucki and Brower 1992, Zalucki and Malcolm 1999). Cardenolides are a type of steroid-glycoside that include digitoxin; they induce nausea, vomiting, diarrhea, and cardiac arrhythmias in vertebrates. As larvae feed on milkweed, they sequester cardenolides for use as a chemical defense against natural enemies (Brower 1984). Cardenolide levels vary both within and between milkweed species and are inducible by damage or herbivore feeding (Malcolm and Zalucki 1996). While monarch feeding on many milkweed species has been documented, our knowledge of how monarch survival is affected by the female s choice of host plants is incomplete. 13

16 Milkweed grows in a variety of disturbed and undisturbed environments, including farmlands, along roadsides and in ditches, open wetlands, dry sandy areas, short- and tall-grass prairie, agricultural areas, river banks, irrigation ditches, and arid valleys. Many species, especially Asclepias incarnata (swamp milkweed), Asclepias curassavica, (tropical milkweed, or bloodflower) and Asclepias tuberosa (butterfly weed), are often planted in gardens. Asclepias curassavica (tropical milkweed) Livestock pastures can also represent significant milkweed habitat for monarchs. Some milkweeds are toxic to livestock (Malcolm 1991), especially if they are included in harvested livestock feed. However, the bitter taste of cardenolides in milkweeds may deter livestock sufficiently that milkweeds are not a serious problem when growing wild in pastures. Thus it is common to see extensive milkweed growth in pastures throughout North America, and these plants may be an important food resource for monarchs. Asclepias syriaca (common milkweed) Woodson (1954) provides a good background on the distribution of milkweed species in the United States and Canada, but less is known about their distribution in Mexico. The most widely-used monarch host plant in the northern United States and Canada is the common milkweed, Asclepias syriaca (Malcolm et al. 1989), which thrives in disturbed areas and has probably been particularly successful following the development of agriculture in the grasslands and former forests in the central and northeastern United States and southeastern Canada (Malcolm et al. 1989, Vane-Wright 1993, Brower 1995). Because it thrives in disturbed habitats, natural plant succession affects common milkweed distribution and abundance. Asclepias viridis, Asclepias asperula and Asclepias oenotheroides are important host plants in the southern United States. Asclepias currassavica is probably the most important host species in Mexico, but Montesinos (2003) reports also finding eggs and larvae on Asclepias glaucescens in the state of Michoacán. Close-up of common milkweed blossoms Milkweed pollination is accomplished in an unusual manner. The pollen is contained in structures called pollinia (pollen sacs), rather than occurring as free grains as is the case for pollen in the rest of the Apocynaceae. Pollinia attach to hairs or bristles on the feet or heads of visiting insects, and are carried to the receptive surfaces of other milkweeds. The most effective milkweed pollinators are large wasps, although bees, moths and butterflies can also carry the pollen from plant to plant. Of those milkweeds that have been studied, the majority are self-incompatible, which means that they must receive pollen from other milkweeds of the same species to produce viable seeds. Asclepias syriaca and its close relative, Asclepias speciosa, have a peculiar root system that ramifies underground, and can cover thousands of meters. It is possible that a single plant (known as a genet) can form hundreds, and possibly even thousands of stems (known as ramets) that are genetically identical. Underground root-like stems of an Asclepias syriaca genet in Michigan. The vertical stakes are 0.5m apart and soil was washed away with water. 14

17 5 The Monarch Butterfly s Annual Life Cycle North American monarchs form two fairly distinct populations. The western migratory population breeds in the western United States and Canada, and winters near the California coast. The eastern migratory population breeds in the central and eastern United States and in southern Canada, and winters in central Mexico (in the eastern part of the state of Michoacán and western part of the state of México). The monarchs that spend the winter in the mountains of central Mexico or eucalyptus groves of coastal California are the final generation of a cycle that begins anew each year. Most of the butterflies in this final generation begin their lives as larvae in the northern United States or southern Canada, and then migrate up to thousands of kilometers to specific overwintering sites. After spending several months at these sites, they fly north and east, starting the cycle again. Butterflies that are part of the eastern population lay eggs in northern Mexico and the southern United States. These eggs become the adults that re-colonize the northern part of the breeding range (Malcolm et al. 1987, 1993), and the population undergoes two more breeding generations. Only the final generation of the year migrates to Mexico in the fall. The behavior of the western population is similar, although the generation that overwinters probably re-colonizes most of the summer range, with subsequent generations increasing in numbers over the summer. Spring and summer adults live about a month, and those that migrate and overwinter live up to seven to nine months. 5.1 Migration Although they live in temperate regions during the summer, monarch butterflies, like other Danainae, are essentially a tropical species. Unlike other temperate insects, no life stage of the monarch butterfly can survive temperate-zone winters. Every autumn, North American monarchs undergo a southward migration to winter roosting sites, and re-colonize their breeding range the following spring. The monarch is the only butterfly to make such a long, two-way migration, with most of those in the east flying over 2500 kilometers (km) to reach their winter destination. Migratory individuals are typically in reproductive diapause, a state of suspended reproductive development that is controlled by neural and hormonal changes (Herman 1981) triggered by environmental changes, including decreasing day length, increasingly cooler nights, and, perhaps, host plant senescence (Goehring and Oberhauser 2002). Since the discovery of the wintering sites in Mexico by the scientific community in 1975 (Urquhart 1976), researchers have struggled to understand the cues that cause monarchs to begin their migration, the mechanisms they use to orient and find the overwintering sites and the patterns of fall and spring flights (Solensky 2004, Zhu et al. 2008). Although they live in temperate regions during the summer, monarch butterflies, like other Danainae, are essentially a tropical species. Monarch migration appears to be a fairly flexible behavior that changes in response to new environments. For example, Australian monarchs sometimes exhibit seasonal movement, moving from inland to coastal areas in a north to northeasterly direction during the fall and winter (James 1993). Hawaiian, Caribbean, Mexican and South American populations do not migrate. Because the most spectacular monarch migrations occur in the eastern North American population, much of the research on monarch migration has focused on this population. These butterflies fly from their summer breeding range, which spans more than 100 million hectares (ha), to winter roosts that cover less than 20 ha, often to the same forest sites, year after year. 15

18 Nectar sources are vital to monarchs during their fall migration, when they need carbohydrates to fuel their flight and to convert to the lipid reserves or fat that supports them during the winter (Brower 1985, Masters et al. 1988, Gibo and McCurdy 1993, Brower et al. 2006). A variety of flowering plants are used during the fall migration; of particular note are goldenrods (Solidago spp.), asters (Aster spp.), and gayfeathers (Liatris spp.) in the north, and frostweed (Verbesina virginica) in Texas. Blooming clover, sunflower and alfalfa fields can also host thousands of monarchs (K. Oberhauser, E. Howard, personal observation). Overwintering monarchs form dense clusters on the branches and trunks of trees, and large aggregations of butterflies in a discrete area are called a colony. While it has often been assumed that the eastern and western North American populations are strictly separated by the Rocky Mountains, recent evidence suggests that some western monarchs move south and southeast, entering the Mexican state of Sonora from Arizona (Pyle 2000, Brower and Pyle 2004). It is possible that some degree of genetic interchange occurs in Mexico and within the Rocky Mountains during the breeding season, preventing complete separation of the two populations. 5.2 Overwintering Mexico The eastern monarchs spend the winter in a temperate mountain ecosystem in Mexico dominated by oyamel firs (Abies religiosa) (Brower 1995). Overwintering monarchs form dense clusters on the branches and trunks of trees, and large aggregations of butterflies in a discrete area are called a colony. Their colonies range in size from 0.5 to 5 ha, and occur on 12 different massifs (discreet mountainous masses) in the Transverse Neovolcanic Belt, a belt of volcanic mountain ranges and valleys extending across central Mexico (approximately 19 N and 100 W) (Calvert and Brower 1986, Slayback et al. 2007). The majority of the colonies are within the federally protected Monarch Butterfly Biosphere Reserve (MBBR), administered by the National Commission of Natural Protected Areas (Conanp). The high altitude forests provide a cool microhabitat for monarchs, which results in a low metabolic rate and reduced activity for the butterflies, from mid-november to mid-march (Brower 1996). Overwintering colonies are spread over an area approximately 100 km x 100 km (Calvert and Brower 1986), but recent analyses show that the appropriate microclimatic conditions occur in approximately 562 km 2 of the entire 10,000 km 2 region (Slayback et al. 2007). Within the suitable area, individuals sometimes settle on the same stands of trees as their predecessors did in the previous winter and, in other years, they may settle up to 1.5 km away (Slayback et al. 2007). Although no formal scientific studies have been published on the importance of access to water by overwintering monarchs, there are many indications that access to moisture is of key importance. Monarchs form colonies at the heads of the streams, and as the dry season advances and the stream sources drop down the arroyos (valleys), the monarch colonies move down, presumably to avoid desiccation (Calvert and Brower 1986). Additionally, massive flights out of the colonies to drink at natural water sources occur regularly and with increasing frequency as the dry season advances. Literally millions of monarchs fly out of their colonies and alight along moist stream banks and water seeps where they drink. The butterflies also drink moisture that condenses as frost on the open llanos (meadow) vegetation. The guides at the tourist facility at the El Rosario colony have taken advantage of this fact, piping water from springs and spraying it over vegetation which is then visited by thousands of monarchs, to the delight of visiting tourists. Lincoln Brower (personal communication) notes that southwestern winds that blow across the volcanic plain often result in adiabatic condensation of clouds (changing in temperature without heat 16

19 Migratory Routes of the Monarch Butterfly Spring fall Monarch butterfly habitat Migration direction Light migration Population zones Source: Maps based on research by Lincoln Brower, Sonia Altizer, Michelle Solensky and Karen Oberhauser, with reference to maps of Journey North and Texas Monarch Watch 17

20 loss to or gain from the surrounding air) as the winds are forced up over the Chincua mountain range. Oyamel fir needles are often covered with moisture, and during adiabatic events, in a phenomenon known as fog drip, water drops fall from the trees onto the ground. This phenomenon is well known in the California redwood forests, where it accounts for a significant proportion of the entire ground water recharge California Prior to European settlement, overwintering monarchs presumably used native forests along the California coast. Deforestation taking place in coastal California in the 19th century led to a decline in overwintering habitat for monarchs. Subsequently, pine forests were largely replaced by Eucalyptus trees, introduced in the 1850s for landscaping, as windbreaks, and for use as fuel (Lane 1993). Now, coastal California monarch wintering sites consist of wooded areas most often dominated by the non-native eucalyptus (Eucalyptus spp.), although monarchs also use the native Monterey pines (Pinus radiata), Monterey cypresses (Cupressus macrocarpa) and redwoods (Sequoia sempervirens) when these species are present. The sites are typically located in sheltered bays or farther inland, where they provide moderated microclimates and protection from strong winds. More than 300 different aggregation sites have been reported (Frey and Schaffner 2004, Leong et al. 2004), with high degrees of year-to-year fidelity to specific locations. As is true of the monarchs overwintering in Mexico, access to water, particularly early morning dew, appears to be important to winter survival Winter Breeding Populations Small, non-migrating populations persist for most years in southern Florida (Knight et al. 1999, Altizer et al. 2000). It is likely that they are periodically extirpated, due to low temperatures, and receive an influx of migratory individuals from the eastern migratory population each fall (Knight et al. 1999). These individuals, as well as the monarchs of Cuba (Dockx 2007), probably do not represent a separate population. Resident populations have also been reported in Texas and other Gulf Coast states, and may be becoming more common (K. Oberhauser and R. Batalden personal observation). These populations are probably temporary, and may represent individuals from the migratory population that do not continue on to Mexico. Additional small, ephemeral populations are found during the winter along the southern Atlantic Coast and the Gulf Coast of the southern United States, but the source and breeding status of these populations are poorly understood. Monarchs breed throughout the year in the Mexican states of Morelos, Guerrero, México, Oaxaca, Veracruz, San Luis Potosí, Chiapas, Michoacán, and Hidalgo (Montesinos 2003). Montesinos (2003) reports finding eggs and larvae on Asclepias curassavica in all of these locations, and on Asclepias glaucescens in Michoacán. The degree to which these local populations interbreed with the migratory butterflies is unknown. Butterflies in forest 18